Ultimate behavior of steel beams under non-uniform bending

The ultimate behavior of steel beams deeply influences the overall performance of steel frames. The main response parameters are the rotation capacity and the flexural ultimate resistance. The former is the source of the local ductility supply needed to achieve a global dissipative behavior of structures under seismic actions, whereas the latter governs the flexural overstrength whose knowledge is needed for an appropriate application of hierarchy criteria in seismic design of structures. Therefore, a twofold classification of steel members according to their ductility and overstrength is the most appropriate approach for seismic design applications. Currently, modern international design codes are based on the classification of steel sections for both plastic and seismic designs of structures, providing misleading emphasis mainly on local buckling as the primary strain-weakening effect. Even though different methods are available in the technical literature for predicting the ultimate behavior of steel members under non-uniform bending, the problem still deserves further investigations, because of the high number of parameters affecting the ultimate response and the variety of cross-sectional shapes. Therefore, a new experimental program dealing with a wide range of cross section typologies (I and H sections, Square and Rectangular Hollow sections) under monotonic and cyclic loading has been carried out by testing specimens with different local slenderness ratios properly selected to integrate the data already available in the technical literature. The obtained results are herein presented and discussed.